linux-kernel - Re: [PATCH v8 01/11] cpuidle/poll_state: poll via smp_cond_load

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Message-ID: <Zw-QM07-9IdV-yIw@arm.com>
Date: Wed, 16 Oct 2024 11:06:43 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-pm@...r.kernel.org, kvm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	will@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
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	joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
	konrad.wilk@...cle.com
Subject: Re: [PATCH v8 01/11] cpuidle/poll_state: poll via
 smp_cond_load_relaxed()

On Tue, Oct 15, 2024 at 02:32:00PM -0700, Ankur Arora wrote:
> Catalin Marinas <catalin.marinas@....com> writes:
> > I'd say if you want
> > something like this, better introduce a new smp_cond_load_timeout()
> > API. The above looks like a hack that may only work on arm64 when the
> > event stream is enabled.
> 
> I had a preliminary version of smp_cond_load_relaxed_timeout() here:
>  https://lore.kernel.org/lkml/87edae3a1x.fsf@oracle.com/
> 
> Even with an smp_cond_load_timeout(), we would need to fallback to
> something like the above for uarchs without WFxT.

Yes, the default/generic implementation would use cpu_relax(). For the
arm64 one, some combination of __cmpwait() and __delay() with the
fallback to cpu_relax().

-- 
Catalin